Process control systems, like those used in chemical, petroleum or other processes, typically include pipes through which the flow of fluid or gas is adjusted by opening or closing valves. The valves are controlled by one or more process controllers communicatively coupled to one or more field devices via analog, digital or combined analog and digital signal transmission links called buses. The field devices may be, for example, valve positioners, switches and transmitters (e.g., transmitters of information from sensors of temperature, pressure, fluid level, flow rate, and valve stem position). The field devices are located within a process plant environment and perform process functions such as opening or closing valves, measuring process parameters, gathering diagnostic data, etc.
The process controllers may or may not be located within the process plant environment. They receive signals representing process measurements made by the field devices, and/or other information pertaining to the field devices, and they execute a controller application. The controller application runs, for example, different control modules which (a) make process control decisions, (b) generate control signals based on the received information, and (c) coordinate with control modules that are performed by processors located in the field devices. The control modules in the controller send the control signals over the transmission links to the field devices to thereby control the operation of the process.
Information from the field devices and the controller is usually made available over a communication link to one or more other hardware or software devices, such as operator workstations, personal computers, data historians, report generators, centralized databases, etc., typically placed in control rooms or other locations away from the harsher plant environment. These hardware devices run applications that may, for example, enable an operator to perform functions with respect to the process, such as changing settings of the process control routine, modifying the operation of the control modules within the controller or the field devices, viewing the current state of the process, viewing alarms generated by field devices and controllers, simulating the operation of the process for the purpose of training personnel, testing the process control software, keeping and updating a configuration database, etc., or testing or gathering data about any of the devices of the process control system, such as any type of valve used in the process control system.
A valve used in the process control system conventionally comprises, as components, a valve seat and a valve closing element which engages the valve seat to close the valve. When these components engage properly, there is a proper valve closure, and the valve has a satisfactory valve seating integrity. Through repeated use in operations of the process control system the valve components may deteriorate due to normal wear, erosion, corrosion, etc. By observing how the valve components work together, a judgment can be made of the soundness and condition of these components. The soundness and condition of the combination of valve components and their operation may be referred to as the valve seating integrity of the particular valve, sometimes also referred to as a valve signature profile. It is desirable to detect when the valve seating integrity is compromised because, when this occurs, the valve may not close properly, thus creating problems with the overall system. For example, leakage may occur when the valve seating integrity is compromised.
Another more specific example of what problems may arise as a result of deterioration in the valve seating integrity is in the case where a process plant system uses high pressured steam to generate power (e.g., 1000s of psi). A valve may be used to regulate the flow of the steam in the power generation system. If there is a problem with the valve, for example, a component of the valve is slightly eroded, then when a high amount of steam pressure is put through the valve, the slightly eroded component may quickly erode to a level where the uncontrolled high pressured steam becomes a danger in the system. In addition to the further damage that may occur to the valve seating components and the detrimental effect to the operation of the process control system, financial loss may also occur. In particular, financial loss may result from the loss of energy that is wasted through a valve with a poor seating integrity. Therefore, it is may be extremely important to find a problem with the valve seating integrity as soon as possible.
Conventional tests to check the valve seating integrity include acoustic valve tests and valve signature tests. Acoustic valve tests are designed to generate an acoustic signal in the vicinity of the valve as gas or liquid materials flow through the valve. With conventional acoustic tests, the structure-borne noise spectrum data indicating the sound level and sound frequency of a valve in good condition differs noticeably from the data obtained from a valve that is deteriorating beyond an acceptable level. These acoustic valve tests are computation intensive and require additional hardware, and are thus expensive to implement.
Conventional valve signature tests are used to detect valve problems, such as valve stem integrity, worn out seat components, the crossing of maximum or minimum friction thresholds, torque thresholds, seat positioning problems, seat erosion problems, and stick-slip conditions. However, conventional valve signature tests require either interrupting the process during the test or blocking in (i.e., isolating) the valve to avoid a process interruption. Additionally, the valve signature test requires a user to perform the test and to visually inspect and interpret the test results. The results produced by the valve signature test provide a plot of valve stem position versus pressure. A user generally needs to be experienced with valve signature graphs to determine when there is a problem. In addition to the need of an experienced user to interpret the results, the valve signature test is difficult to run and interpret every time a valve moves to or from the seating position.
Overall, conventional tests used to determine valve seating integrity require human intervention and analysis, and/or may require stopping the process control operation. In particular, a conventional valve signature test requires human intervention and analysis along with having to either (1) interrupt the process control system to perform the valve signature test as part of a maintenance routine or (2) implement block and bypass valves into the process control system, so that the block and bypass valves may be used to reroute the flow of material (e.g., liquid or gas) through the plant as the isolated valve is being tested. The block and bypass valves may also be referred to as isolation valves.
In case (1) the process plant may lose a considerable amount of production. In case (2) the plant owner has to initially invest a considerable amount of resources to implement the block and bypass valves and to invest in the man power that is required to operate the block and bypass valves when performing a seating integrity test on the valve. In particular, a user that is physically located near the bypass valve must coordinate with another user that manages the operational switch from the valve to the bypass valve. The user that is physically located near the bypass valve must manually turn open the bypass valve in accordance with directions from the managing user. After the operational switch to the bypass valve is complete, the user must manually secure and verify whether the valve is blocked out of the process. The user secures and verifies that the valve is blocked out of the process by turning the two block valves that are located at each end of the valve that is to be tested. The isolation of the valve requires additional valves, additional man power, and considerable worker coordination and time.
Moreover, because of the added cost, loss in production, and the additional labor that is involved when using the conventional valve seat seating integrity tests, the tests are not often run. Typically, the valve seating integrity tests are run once a year or every five years. With the disclosure provided below, similar tests results may be produced more frequently and/or may be produced without the problems described herein that are associated with conventional valve seat seating integrity tests.